Bit assembly for a down-the-hole hammer drill

ABSTRACT

The invention provides for a down-the-hole drill bit assembly comprising a drill bit having a screw-thread at its anvil end, external splines on the drill shank and co-operating splines within a drill casing as well as a co-operating screw thread carried by a component within the casing. The assembly is arranged to have engagement of the splines with the screw threads disengaged for driving the drill and to have the screw threads engaged and splines disengaged to permit removal of the bit from the assembly.

FIELD OF THE INVENTION

Hammer drills operating down-the-hole are well known and widely used and usually pneumatically powered.

BACKGROUND TO THE INVENTION

A long persistent difficulty with many different designs of these hammers is the difficulty in removing the bits when necessary for replacement or repair. This difficulty is compounded in large cluster drills where the multiplicity of drills are used in a single canister. Use of drills currently available frequently result in the bit or bits binding on their mountings to such an extent that the latter are frequently seriously damaged before the bits are released. This increases the time and expense of down time resulting from this problem.

OBJECT OF THE INVENTION

It is the object of the invention to provide a design in which this problem is largely overcome.

SUMMARY OF THE INVENTION

According to this invention there is provided a down-the-hole drill bit assembly comprising a drill bit having a screw-thread at its anvil end, external splines on the drill shank and co-operating splines within a drill casing and a co-operating screw thread carried by a component within the casing, the assembly being arranged to have engagement of the splines with the screw threads disengaged for driving the drill and the screw threads engaged and splines disengaged to permit removal of the bit from the assembly.

The invention also provides for the screw thread to be on the drill bit shank or within a bore in the anvil end of the drill shank; for the splines within the drill casing to be part of the casing or part of a chuck member securable within the casing; for the co-operating screw thread on the outside of the shank, to be inside a chuck or for the co-operating threads inside the shank to be on a fixed or axially movable control member.

A hammer drill bit chuck is also provided comprising at is operatively upper end a bush at the lower end of which is an internal thread, internal splines extending below the thread having an internal diameter greater than the internal diameter of the thread, the external surface of the chuck providing a seat for a wear sleeve and operatively above the seat an external screw thread adapted to engage an internal screw thread in a wear sleeve.

This aspect of the invention provides a hammer drill bit having a drill head adapted to operatively engage the bottom of a drill chuck, external splines set back from the drill head and adapted to engage internal splines in a complementary shaped drill bit chuck having an internal screw thread with an internal diameter less than that of the external splines on the bit and the end of a drill shank having an external screw thread along part thereof adjacent its bit anvil to engage and pass through a complementary screw thread in the drill bit chuck.

The invention also provides the drill bit assembly of the chuck and drill bit as defined in the end of the wear sleeve.

A further feature of the assembly of this invention provides for the bottoms of the internal splines in the chuck and external splines on the bit each are shaped as one turn of a helical cam with a pitch equal to that of a screw thread in the chuck to provide at their ends engaging surfaces to rotate the bit with the chuck.

According to alternative features of this invention there is provided a hammer drill bit assembly wherein the bit has a screw thread extending from the anvil and which is engageable with a complementary screw thread on a bit mounting such that the engagement of the screw threads provides for the bit to be moved into and out of limited sliding engagement with the mounting by the passage of screw threads one though the other.

Yet further features of the invention provide for the bit and bit mounting carry mating splines engaged when the screw threads have passed one through the other and for the mounting to be a chuck or a control rod in which assembly the screw threads will be externally on the rod and within a bore provided in the anvil end of the bit.

According to a further embodiment of this invention a hammer drill assembly has a bit with a series of splines along its shank and a screw thread within an axial bore extending from the anvil end of the shank, a series of internal splines extending from the end of the assembly wear-sleeve to co-operate with the splines on the bit shank and a rod in the assembly with a screw thread engageable with the screw thread in the shank and means for sliding the rod relative to the bit to engage and disengage the splines.

Also, the invention provides for the rod to be a distributor control rod extending from the backhead of the assembly, for the drill assembly to be a cluster drill including assemblies as above defined wherein the rods are individually or collectively movable.

This aspect of the invention provides for the screw threads are disengageable to permit the bit to be moved around the rod to index its position in the assembly and engaged to release the bit from the assembly.

A still further feature of this invention provides for the co-operating screw threads to be replaced by a resilient retainer ring in a chuck or drill casing co-operating with wedge formations on the bit shank to retain or release the bit under resilient axial pressure applied to the bit through a control rod or other component.

Further features of this embodiment provide for the ends of the splines and the upper and lower edges of the inner surface of the split ring to be tapered and for the end of the control rod and upper surface of the bit to be shaped to provide axial alignment when contacted together.

The invention also provides for the retainer ring to be supported in a grooved chuck carried by the drill casing.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the invention will become more apparent from the following description of several embodiments of the invention; by way of example only; with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal cross section through a drill chuck;

FIG. 2 is a longitudinal cross section through a drill bit assembly;

FIG. 3 shows two relative positions of the bit when not in use and;

FIGS. 4 and 5 are diagrammatic views of modified component;

FIG. 6 is a cross section of a different hammer drill including this invention in drilling mode and;

FIG. 7 is a cross section of a hammer in flushing mode;

FIG. 8 illustrates one method of sliding a control rod relative to a bit in a hammer drill assembly; and

FIG. 9 illustrates one alternative to the use of screw threads threading through each other.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the chuck (1) has a bit head engaging end (2) providing an external annular seat (3) for the end of a drill assembly wear sleeve (10) shown in FIG. 2. Above the seat (3) is an external screw thread (4) for securing the chuck (1) to the end of the wear sleeve (10).

Annular passages (5) are provided opening through ports (6) into the chuck (1) for flushing fluid through or around the bit when the drill assembly is raised off its operating position. An internal screw thread (7) of about four pitches extends upwardly from the ports (6) towards the upper end of the chuck (1). Above the thread (7) the inner wall of the chuck (1) provides a bit guide (8). For a tubeless design of bit assembly a stem bush will be provided for the bit guide (8). Internal bit rotating splines (9) extend downwardly from ports (6) to about halfway between the wear sleeve seat (3) and the lower end of the chuck (1).

Referring now to FIG. 2, the chuck (1) is shown in a drilling assembly. The wear sleeve (10) is shown screwed onto the chuck (1) with a drill bit (11) in the operational drilling position. The chuck (1) is supported on the stepped drill bit head (12).

The bit shank (13) carries splines indicated at (14) which engage the splines (9) in the chuck (1).

Stepped back from the upper end of the drill shank (13) the shank carries an external screw thread (15) complementary to the screw thread (7) in the chuck.

The shank is shown to include an exhaust tube (16) for the drilling operating fluid.

In the drilling position of the assembly shown in FIG. 2 the screw threads (7) and (15) are disengaged and longitudinally spaced apart.

FIG. 3 on the left hand side shows the drill bit (11) about to be engaged in the chuck (1). The shank (13) has been inserted into the chuck (1) by sliding the screw threaded section (15) inside the splines (9).

To reach the engaged position of the bit shank (11) in the chuck (1) the bit thread (15) is screwed through the chuck thread (7). From this position the shank (13) can be moved up through the bit guide (8) into an operating position within the wear sleeve (10) without any screw threaded engagement between the chuck (1) and the bit shank (11). In the operating position the splines (14) on the bit are engaged into the splines (9) on the chuck (1).

The assembly described enables the drill bit (11) to move between an operational and bit flushing condition without the bit (11) sliding out of the chuck (1). This is prevented by the bottom of thread (15) contacting the top of the thread (7). The bit is then removed by screwing the threads (15) and (7) one through the other to release the bit (11).

The assembly avoids the binding of screw threads in use and simplifies assembly and disassembly with consequent savings in downtime and costs.

An alternative embodiment is to not totally disengage the splines from each other when the bit (11) drops down into stopping mode and when the hammer is rotated clockwise the splines (9) in the chuck (1) will still be in driving engagement into the splines (14) on the bit (11). This arrangement is shown in FIGS. 4 and 5. The upper face (17) of the splines (14) on the bit (11) as well as the lower face (18) of the splines (9) on the chuck (1) are machined in the fashion of a cam at the same pitch (19) as the thread (15) on the bit shank for one pitch only. The cam will start and stop opposite the same point on the bit shank (13) and the starting and stopping points will be the distance of one pitch apart.

In this case the threaded bit shank (13) will pass through the splines (9) in the chuck (1) as described above until the thread (15) on the bit shank butts up against the internal thread (7) in the chuck (1) at which stage the splines (9) and (14) are not yet engaged into each other. The bit (11) is now screwed in until there is one thread left in which position the peak point (20) of the cam shaped splines (14) of the bit will be opposite and very close to the peak point (21) of the cam shaped chuck splines (9). One more turn and the thread (15) on the bit head will be through the internal thread (7) of the chuck (1) and since the thread and the cam have the same pitch, the two matched cam shapes will fit into each other with the peak spline on the bit butting up against the peak spline of the chuck and the bit will be driven in a clockwise direction by the chuck.

When the hammer is now lifted out of the hole and hanging in a vertical position the thread on the bit head will be sitting against the internal thread of the chuck and the cam shaped head will engage with the thread in the chuck and the cam shapes will move away from each other causing the splines to be disengaged and the bit may be unscrewed by hand.

The above description applies to a preferred embodiment but it could also be that the thread is before the spline in which case the external spline of the bit will be smaller than the internal thread in the bore of the chuck and the spline will pass through the internal thread first and only after the bit shank is threaded through the internal thread of the chuck then the external spline will mate with the internal spline of the chuck. The thread could also be imposed on top of the spline (i.e. the thread and spline are in the same space) in which case the thread and spline on the bit shank (or in the chuck) could be up to the same diameter. In this case the thread will be imposed on the internal spline of the chuck (or external spline of the bit) and the bit shank will have an external thread which threads through the internal imposed thread on the spline and once it has passed through, the spline on the bit shank will enter and engage the internal (threaded) spline in the chuck.

The above descriptions illustrated show a drill bit assembly for drilling holes without consideration of retaining a drill core. In the case of a hollow bit those skilled in the art will appreciate the invention will be applied with the co-operating components arranged internally. That is, where a hollow bit is used in the drill assembly those skilled in the art will understand that hollow bit will have internal splines and thread and the chuck will have external splines and thread.

Referring now to FIGS. 6 and 7 the down-the-hole hammer drill (101) illustrated includes a control rod (102) arranged as a distribution tube for the supply of pressurized air to drive the drill (101).

The control rod (102) is supported from the backhead (103) in a wear sleeve (104). A piston hammer (105) operates within the wear sleeve (104) on the control rod (102).

A drill bit (106) is supported in the lower end of the wear sleeve (104) and has splines (107) around its upper end to guide the bit movement along a co-operating set of splines (108) within the wear sleeve (104). The bit (106) has a blind bore (109) which communicates with the plurality of flushing passages (110) which open through the face (111) of the bit.

The upper end of the bore (109) carries an inwardly extending screw thread (112).

The free end of the control rod (102) carries an outwardly projecting screw thread (113) which mates with the screw thread (112).

The bit (106) is introduced into the lower end of the wear sleeve (104) by screwing the thread (112) onto and past the screw thread (113) on the control rod (102). The bit (106) then has a limited axial movement along the lower end of control rod (102) but cannot be removed from the rod (102) and wear sleeve (104) without re-engaging the screw threads and screwing the bit (106) over and past the end of the control rod (102). It will be noted that the splines (108) within the wear sleeve (104) are short enough to allow the bit to be rotated for movement along the rod (102) on the screw threads (112) and (113).

FIG. 7 shows the hammer drill (101) in flushing mode where the bit (106) has moved partly out of the wear sleeve (104) and is restrained against further axial movement by the butting of the ends of the contiguously located screw threads (112) and (113).

To restart the hammer drill the bit (106) is moved back into the wear sleeve and the screw threads are separated and the splines (107) and (108) on the bit (106) and in the wear sleeve (104) respectively are re-engaged for normal operation of the drill.

Two major advantages are obtained from the construction and operation of the hammer drill, set out in FIGS. 6 and 7. Firstly no chuck assembly is required and secondly the direct impact of the hammer (105) on the anvil of the bit (106) without any stress being applied to the retaining threads (112) and (113). The latter makes the removal and replacement or repair of the bit to be a simple hand operation.

The embodiment of FIGS. 6 and 7 utilize the screw threads in the bit and on the control rod to fit and release the bit while permitting it to have limited sliding in the assembly when the drill is moved from operative to inoperative conditions.

In FIG. 8 the screw threads (211) and (212) are arranged such that they can be moved into and through each other without releasing the splines (215) on the bit shank from the internal splines (214) in bit assembly wear sleeve.

To enable the latter to take place the control rod (207) is mounted to be axially slideable in the assembly. This enables the rod (207) to move the splines out of engagement without the bit (210) being removed from the assembly. This then enables the bit (210) to be rotated on the control rod (207) to index the drill buttons (213) in the assembly. Moving the rod (207) axially in the reverse direction will reset the assembly for operation. This ease of indexing the drilling buttons (213) is particularly useful in cluster drill assemblies to maintain the gauge of hole drilled without stripping the assembly.

When it is necessary to replace the drill bit (210) the rod (207) is rotated in the bit as set forth above to release the bit from the assembly.

More specifically with reference to the hammer illustrated in FIG. 8 this is suitable for use as one of a cluster drill assembly. As shown the hammer is to be mounted in the drill canister (not shown) along with the arrangement of other drills.

The hammer (201) has a shoulder (202) at the top and another (203) at the bottom of the chuck (204) forming part of the piston casing (205). These shoulders enable the hammer to be clamped between the plates of the lid and base (not shown) of the canister. In this particular example a ram piston (206) is provided above the control rod (207). An air supply is provided through inlets (208) to force the ram piston (206) down thus forcing the control rod (207) down.

There is a spring set (209) to return the control rod (207) to its original position when air pressure is relieved. In use when the bit (210) is allowed to drop forward the bit (210) will remain retained in the splines with the stop threads (211) and (212) against each other.

When the control (207) rod is pushed forward with respect to the piston casing (205) the bit (210) will drop past the splines and not be locked for a rotational movement in the casing (205).

In this orientation the bit (211) may rotated step wise to enable the drill buttons (213) to be indexed around the periphery of the hammer or unscrewed for removal.

The movement of the control rod may of course be effected by other means which include means for moving all the hammer bits of the cluster drill collectively should this be a desirable feature. Also the hammers may be located and held in the canister in other ways than by the shoulders as described. The use of the casing (205) to provide the drill chuck (204) with the internal splines (214) is a convenient assembly which can of course be provided in a chuck separate from the casing (205) if desired.

Referring now to FIG. 9 of the drawings the hammer assembly (301) shown is suitable for cluster drills. The assembly (301) includes a drill casing (302) with a chuck (303) mounted to the lower end of the drill casing (304). The chuck (303) and top closure (305) of the casing are provided with shoulders (306) and (307) to facilitate a multiplicity of assemblies being mounted between the end plates of a cluster drill cannister (not shown).

The assembly includes a control rod (308) mounted on a spring biased piston ram (309).

The drill bit (310) has splines (311) provided around the free end of the shank (312) and these splines have tapered ends as shown at (313). The bit (310) has a stepped head (314) enabling it to seal against the bottom of the chuck (303).

The bit is slidably retained in the chuck by a split resilient retainer ring (315). This ring (315) is made of inherently resilient steel and the top and bottom inner edges (316) of the ring are tapered. These tapers co-operate with the tapers (313) to enable the drill bit (310) to be introduced and removed from the assembly.

The bit (310) has an axial blind bore (317) with the outer end tapered. The control rod (308) also has its free end tapered to centralize axial pressure applied by the rod (308) on the axial end of the bit (310).

As shown the control rod (308) can be pushed down to move the bit (310) so the splines (311) will spread the ring (315) to release the bit from the chuck (303). Before the releasing process is started the bit (310) will be dropped down the splines (311) to the inoperative position.

To replace the bit (310) the drill assembly will be placed over the rigidly held bit and moved downwardly. The tapered free ends of the splines (311) will spread the retainer ring which will contract behind the splines (311) to place the bit ready for drilling.

The embodiments described all enable the drill bit assemblies to be used without binding of the bit and thus provide ease of replacement or repair. 

1. A down-the-hole drill bit assembly comprising a drill bit having a screw-thread at its anvil end and splines and cooperating splines and a cooperating screw thread carried by a component within the casing, the assembly being arranged to have engagement of the splines with the screw threads disengaged for driving the drill and the screw threads engaged and splines disengaged to permit removal of the bit from the assembly.
 2. A drill bit assembly as claimed in claim 1, in which the screw thread and splines are on the drill bit shank.
 3. A drill bit assembly as claimed in claim 1, in which the screw thread is within a bore in the anvil end of the drill bit shank.
 4. A drill bit assembly as claimed in claim 1, in which splines are an integral part of the casing.
 5. A drill bit assembly as claimed in claim 1, in which the splines are an integral part of a chuck member secured in the casing.
 6. A drill bit assembly as claimed in claim 1, in which the cooperating threads are inside a chuck.
 7. A drill bit assembly as claimed in claim 3, in which the cooperating threads are on a fixed, rotary or axially movable control member.
 8. A chuck for a drill bit assembly as claimed in claim 1, comprising at its operatively upper end a bush at the lower end of which is an internal thread, internal splines extending below the thread having an internal diameter greater than the internal diameter of the thread, the external surface of the chuck providing a seat for a wear sleeve and operatively above the seat an external screw thread adapted to engage an internal screw thread in a wear sleeve.
 9. A drill bit assembly having a drill head adapted to operatively engage in the bottom of a drill chuck, external splines set back from the drill head and adapted to engage internal splines in the chuck having an internal screw thread with an internal diameter less than that of the external splines on the bit and the end of a drill shank having an external screw thread along part thereof adjacent its bit anvil to engage and pass through a complementary screw thread in the drill bit chuck.
 10. A drill bit assembly as claimed in claim 9, in which the bottoms of the internal splines in the chuck and external splines on the bit each are shaped as one turn of a helical cam with a pitch equal to that of a screw thread in the chuck to provide for rotation of the bit with the chuck.
 11. A drill bit assembly as claimed in claim 1, in which the bit has a screw thread extending from the anvil and which is engageable with complementary screw thread on a bit mounting such that the engagement of the screw threads provides for the bit to be moved into and out of limited sliding engagement with the mounting by the passage of screw threads one though the other.
 12. A drill bit assembly as claimed in claim 11, in which the bit and bit mounting carry mating splines engaged when the screw threads have passed one through the other.
 13. A drill bit assembly as claimed in claim 12, in which the mounting is a chuck or a control rod in which assembly the screw threads will be externally on the rod and within a bore provided in the anvil end of the bit.
 14. A drill bit assembly as claimed in claim 1, which the bit has a series of splines along its shank and a screw thread within an axial bore extending from the anvil end of the shank, a series of internal splines extending from the end of the assembly wear-sleeve to cooperate with the splines on the bit shank and a rod in the assembly with a screw thread engageable with the screw thread in the shank and means for sliding the rod relative to the bit to engage and disengage the splines.
 15. A drill bit assembly as claimed in claim 14, in which the rod to be a distributor control rod extending from the backhead of the assembly, for the drill assembly to be a cluster drill including assemblies above defined wherein the rods are individually or collectively movable and rotatable.
 16. A drill bit assembly as claimed in claim 15, in which the screw threads are disengageable to permit the bit to be moved around the rod to index its position in the assembly and engaged to release the bit from the assembly.
 17. A down-the-hole drill bit assembly comprising a casing supporting in its operative end a resilient split retainer ring and a drill bit shank carrying splines around its anvil end for sliding engagement in co-operative splines in the casing to open the split ring for passage of the bit shank splines into and out of the casing.
 18. A down-the-hole drill bit assembly as claimed in claim 17, in which the ends of the splines on the bit shank and the upper and lower edges of the inner surface of the split ring are tapered.
 19. A down-the-hole drill bit assembly as claimed in claim 17, in which the operative end of the casing is provided by a chuck.
 20. A down-the-hole bit assembly as claimed in claim 17, in which is included a slideable control rod with a free end engageable with free end of the bit anvil to move the bit shank through the retainer ring. 